when drawing plans and sections the technical way of illustrating the many materials we have is by hatching them.
I believe this function, for plusspec, is best done in layout.
is there a tutorial or guide on placing sketchup fills within the “sectional cut” on these detailed drawings?
is there a tutorial or guide on creating your own fill patterns, for this purpose?
Yes this is best done in layout. There currently are no tutorials regarding this but we are in progress of new tutorials at the moment. Take a look at the PlusSpec showcase and you will see hatching on the jobs. There is a direct link below.